1. Field of Invention
The present invention relates to a video signal processing circuit. More particularly, the present invention relates to a processing circuit for processing horizontal and vertical synchronization signals.
2. Description of Related Art
There are various types of horizontal and vertical synchronization signals in the VGA Spec. They are designed to meet requirements of different display systems. The horizontal and vertical synchronization signals can be mutually independent, or combined in a single synchronization signal. FIG. 2 shows examples of different types of horizontal and vertical synchronization signals. Regarding type A, the horizontal synchronization signal 202 is independent of the vertical synchronization signal 204. Regarding type B, the horizontal synchronization signal 206 is combined with the vertical synchronization signal 208, but the vertical synchronization signal 208 still exists. Regarding type C, the horizontal synchronization signal 210 is combined with the vertical synchronization signal 212, and the vertical synchronization signal 212 doesn't exist on a vertical synchronization signal input line.
Video signals from different computers are received and transferred in a keyboard-video-mouse (KVM) system. Conventionally, a specific KVM system is designed for specific types of horizontal and vertical synchronization signals. It is inconvenient and inefficient for different KVM systems to meet different requirements.